1. FIELD OF THE INVENTION
This invention relates to a molding method for manufacture of resin moldings and, more particularly, a resin molded part having movable projections suitable for use in such applications as, for example, a remote control unit or the like control element for a TV set or video tape recorder, and a keyboard for a portable electronic calculator.
2. DESCRIPTION OF THE PRIOR ART
Such control element or keyboard has a number of push-buttons and is generally of such arrangement that the push-buttons, upwardly biased by internally provided springs, are depressibly seated in corresponding holes provided in a base. However, such arrangement has a drawback that it requires a large number of parts, which often leads to a high cost of manufacture.
In view of this problem, some users have been employing molded parts in which a base and pushbuttons are integrally formed. Molded parts of this type use rubber as a molding material therefor and they are such that one or more pushbutton-shaped thick projections are formed integrally with a base through the intermediary of thin wall portions continued from the peripheral edges of the projections so that the projections are flexibly movable.
True, such rubber moldings involve less number of parts; on the other hand, however, the fact that they require vulcanization poses a problem that the process of molding takes considerable time, which means lower producting. In an attempt to solve this problem, it has been proposed to use a resin which requires no vulcanization and which permits ease of molding and to carry out integral molding by employing a conventional side-gate type mold, for example. However, such attempt has not been successful, since they involve high possibility of burrs and sink marks being produced because of unfavorable heat balance between thick projections and thin wall portions.